In the area of engine management for gasoline and diesel engines, components representing an inductive load are frequently used such as quantity-control valves of high-pressure pumps or injection valves, for example. These components are typically triggered via a simple switch output stage.
As a result of fluctuations in the vehicle system voltage, the components behave differently, depending on the vehicle system voltage currently available. This changes especially the metering behavior of valves, particularly of injection valves. It is possible to compensate for changes in the metering behavior caused by fluctuations in the vehicle system voltage for example by extending or shortening the triggering times of the affected components accordingly. Since the metering behavior, however, is not necessarily a linear function of the vehicle system voltage, such compensation is costly.
Further there is the danger that, in the event of very high voltages, the current rises to such a magnitude that the stress on the components becomes unacceptably high such that the component must be switched off above a certain voltage. This results in undesirable restrictions of the functionality of the system as a whole.
To reduce the current stresses on a component, there is to an extent the possibility of shortening the switching time. Here there is the risk, however, that a reliable opening or closing of a valve is no longer ensured when switching times are all too short.
German Patent Application No. DE 4444810 describes a control circuit, in which a blower drive motor is triggered by a pulse-width modulation signal (PWM signal), the pulse duty factor of the PWM signal being a function of an adjustable setpoint rotational speed. If the rotational speed deviates from the setpoint rotational speed, for example due to varying electrical voltages, the rotational speed is returned to the setpoint rotational speed via a control circuit by changing the pulse duty factor of the PWM signal.